The present invention relates generally to the collection of radiant energy of solar origin. A particular type of solar energy concentration and collection device is a cylindrical or trough-shaped collector comprised of an energy absorber and one or two opposing reflective side walls. The collector is formed by extending the transverse cross sections of the absorber and the reflective wall or walls longitudinally, parallel to an axis, to form the trough-like structure. There has been determined the "ideal side wall contour" to achieve maximum concentration of energy incident on the entrance aperture onto the surface of the absorber. The factors which determine ideal side wall contour are the angle of the extreme rays from the radiant energy source, the cross section of the absorber, and the desired maximum angle of incidence less than or equal to 90 degrees of concentrated energy on the surface of the absorber. For energy from an infinite source and for the collection of diffuse radiation, the extreme rays are all equal to a specified acceptance angle selected by the designer and are therefore parallel to each other. For rays from a source of finite dimension and distance from the collector, the extreme rays are those rays generated by the edge points of the source.
U.S. Pat. No. 3,923,381 describes the ideal side wall contour for concentrating energy from an infinite source onto the top surface of a flat energy absorber. U.S. Pat. No. 4,002,499 describes the ideal side wall contour for concentrating energy from an infinite source onto nonflat energy absorbers and onto both sides of flat energy absorbers. U.S. Pat. No. 3,957,031 describes the ideal side wall contour for concentrating energy from a finite source onto an energy absorber of arbitrary shape. U.S. Pat. No. 4,130,107 gives the ideal side wall contour for concentrating energy from an infinite or finite source onto an energy absorber of arbitrary shape wherein the maximum angle of incidence of energy concentrated onto the surface of the energy absorber is restricted to a particular value less than 90 degrees. U.S. Pat. No. 4,114,592 describes the ideal side wall contour for concentrating energy from an infinite or finite source onto an energy absorber of arbitrary shape wherein a refractive medium acts on the rays of incident energy prior to their being concentrated onto the energy absorber. A publication, Applied Optics, Vol. 15, No. 2, pages 291-292, Feb. 1976, describes concentration of radiant energy from an infinite or finite source onto the surface of an arbitrary energy absorber wherein the reflective wall is obtained by total internal reflection within the interface between a dielectric medium and the exterior environment. To the extent the above-cited references contain "essential" material necessary to support the claims hereof or indicate background, they are expressly incorporated by reference herein.
All the designs described above give an ideal contour wherein the side wall or walls terminate by touching the energy absorber. Each side wall includes, for full illumination of the receiver, an involute portion which touches the receiver and then a portion above the involute which directs incident extreme rays so that they intersect the surface of the receiver at a predetermined angle. For a two-walled collector the touching occurs at the cusp of collector wherein the two sides of the reflective walls meet with different slopes. Certain applications preclude the use of a reflective wall or walls which touch the absorber. For example, where the absorber is contained within a glazing to reduce conductive and convective heat loss, it has been determined that one possible technique is to truncate the ideal contour by not including any reflective wall within the glass tube, thereby creating a reflector gap from the full ideal contour. Another approach has been to use the glazing shape to determine the ideal contour rather than the absorber shape.
It is therefore an object of this invention to provide an improved trough-shaped radiant energy concentration and collection device.
Another object of this invention is to provide a concentration and collection device for radiant energy wherein the absorber upon which energy is to be concentrated is contained within a glazing.